We propose to develop a novel cancer therapy using allosteric reagents for concentrating a prodrug around a target cancer cell. Our aptamer-based design, called a CLAMP (cis-linked aptamers for medical or microanalytical procedures), is a nucleic acid with two functionalities with which one can develop allostery. When an allosteric CLAMP binds one of its two targets, it is activated to bind its second target. The activated aptamer can then bind an imaging agent or a therapeutic agent. The property of allostery ensures that the therapeutic agent is only concentrated in locations of high expression of the first CLAMP target. This minimizes the effect of nonspecific interactions that would cause systemic toxicity if the therapeutic agents were directly linked to the CLAMP. Thus, the allosteric CLAMP is expected to be highly selective for the target cells. The allosteric CLAMP will be developed to target metastatic prostate cancer cells and will be designed to require two characteristics of these cells. These characteristics are high expression of prostate stem cell antigen (PSCA) and high expression of the prostate specific antigen (PSA) protease. The allosteric CLAMP will be designed to bind inulin only when it is bound to PSCA. The inulin can be derivatized with a peptido prodrug that is designed as a specific substrate of PSA, which cleaves it to release a toxic agent such as doxorubicin or thapsigargin. The requirement for a combined presence of PSCA and PSA should provide the therapy with high selectivity. Because the allosteric CLAMP will link the cancer cell surface to inulin, the CLAMP-mediated therapy can be seamlessly interfaced with imaging technology by labeling the inulin with a contrast agent such as Tc99m. Being a small nucleic acid, the CLAMP will more readily penetrate solid tissues than will monoclonal antibodies, which are the currently used technologies for selective cell targeting. Thus, we anticipate this technology will provide higher selectivity and higher efficiency of killing prostate cancer cells than current therapies.